As is known, many pourable food products, such as fruit juice, UHT (ultra-high-temperature treated) milk, wine, tomato sauce, etc., are sold in packages made of sterilized packaging material.
A typical example of this type of package is the parallelepiped-shaped package for liquid or pourable food products known as Tetra Brik Aseptic (registered trademark), which is made by folding and sealing laminated strip packaging material.
The packaging material has a multilayer structure substantially comprising a base layer for stiffness and strength, which may comprise a layer of fibrous material, e.g. paper, or mineral-filled polypropylene material; and a number of layers of heat-seal plastic material, e.g. polyethylene film, covering both sides of the base layer.
In the case of aseptic packages for long-storage products, such as UHT milk, the packaging material also comprises a layer of gas- or light-barrier material, e.g. aluminium foil or ethyl vinyl alcohol (EVOH) film, which is superimposed on a layer of heat-seal plastic material, and is in turn covered with another layer of heat-seal plastic material eventually forming the inner face of the package contacting the food product.
Packages of this sort are normally produced on fully automatic packaging machines, on which a continuous tube is formed from the web-fed packaging material; the web of packaging material is sterilized on the packaging machine, e.g. by applying a chemical sterilizing agent such as a hydrogen peroxide solution, which is subsequently removed from the surfaces of the packaging material, e.g. evaporated by heating; and the web of packaging material so sterilized is maintained in a closed, sterile environment, and is folded and sealed longitudinally to form a vertical tube.
The tube is filled with the sterilized or sterile-processed food product, and is sealed and subsequently cut along equally spaced cross sections to form pillow packs, which are folded mechanically to form respective finished, e.g. substantially parallelepiped-shaped, packages.
Alternatively, the packaging material may be cut into blanks, which are formed into packages on forming spindles, and the packages are filled with the food product and sealed. One example of this type of package is the so-called “gable-top” package known by the trade name Tetra Rex (registered trademark).
To open packages of the type described above, various solutions have been proposed, including reclosable opening devices, which substantially comprise a spout, e.g. tubular, defining a through opening and fitted about a hole or a removable or pierceable portion of a wall of the package; and a removable, e.g. screw or hinged, cap fitted to and outwardly closing the spout.
When the opening device is fitted about a hole in the package, the opening of the spout is closed by a membrane made of plastic material, connected integrally to the spout, and detachable from the spout along a preferential, normally circular, tear line. The membrane is normally fixed to the top (i.e. outer) edge of the spout, and is fitted integrally, on the side facing the cap, with a projecting tab, which is pulled off by its free end to detach the membrane from the spout along the preferential tear line and so free the opening to pour out the product.
Though functionally valid, opening devices of the above type still leave room for further improvement, particularly as regards pour-out of the product, which is often irregular and characterized by so-called “gulping”. This is caused when the package is tilted to pour out the product, and the liquid product inside, whose free surface assumes a constantly horizontal position, completely fills the spout, thus isolating the inside of the package from the outside, and so forming a vacuum inside the package which tends to slow down and even cut off outflow. As soon as any change occurs in the above condition, e.g. a change in the tilt angle of the package allowing air inside, outflow of the product is suddenly restored, thus resulting in gulping. And the greater the overall axial dimension of the spout, the greater the range of package tilt angles at which gulping occurs.